Display device

ABSTRACT

The level of a storage capacitor line is changed between two types, an H level and an L level. As a result of this change, the voltage applied to a liquid crystal is shifted so that a sufficient voltage is applied to the liquid crystal to perform a display operation. Then, at least one of two voltage levels of the storage capacitor line is used in common with the potential of at least one of plurality of voltage levels which are used in vertical driver which drives the said selection line. Furthermore, the values of the storage capacitance and parasitic capacitance for the storage capacitor line are set within a specific range.

CROSS-REFERENCE TO RELATED APPLICATION

The entire disclosure of Japanese Patent Application Nos. 2004-152485,2004-152489, 2004-152493, and 2004-152497 including specification,claims, drawings and abstract is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a display device having displaycircuits arranged in a matrix configuration.

2. Description of the Related Art

Conventionally, liquid crystal display devices are known as low powerconsumption display devices that can assume a thinner and morelightweight form and are employed in various types of equipment asdisplay devices. Liquid crystal display devices (hereinafter referred toas LCD) have two substrates with electrodes formed on opposing sidesthereof, laminated with liquid crystals injected between them. A displayoperation is performed by applying a voltage signal across theelectrodes to control the alignment of the liquid crystals, the opticalcharacteristics of which change according to the alignment so as tocontrol the transmissivity of light from a light source.

It is well known that when a DC voltage is continuously applied acrosselectrodes formed on opposing surfaces of the substrates, the alignmentof the liquid crystal molecules becomes fixed, namely, the problem ofscreen burn-in occurs. Thus, an AC voltage signal having a polarity thatperiodically inverts with respect to a reference voltage isconventionally used as the voltage signal for driving the liquidcrystals.

Well known methods for inverting the polarity of the liquid crystaldriving voltage signal in a liquid crystal display device having aplurality of pixels arranged in a matrix configuration are inversion atevery frame, inversion at every vertical scan (1V) or field, inversionat every horizontal scan (1H), and inversion at every pixel (dot). Aframe unit corresponds to a frame in an NTSC signal, for example, and afield unit corresponds to various units (for example, odd fields andeven fields) of a plurality of fields forming one frame.

In Japanese Patent Laid-Open Publication No. 2003-150127, the dotinversion method for inverting the polarity in one-pixel (dot) units ispreferable among the above-mentioned methods as the adverse effect ofinversion on display quality is least likely to appear. However, aproblem was that its driving method is likely to become complex.

It should be noted that modifying the voltage of an SC line, which is aline that becomes a base for a storage capacitance, has been proposed inthe dot inversion method in Japanese Patent Laid-Open Publication No.2003-150127.

SUMMARY OF THE INVENTION

When changing the level of a storage capacitor line in the presentinvention, the potential of at least one level is used in common withthe potential of at least one of either an H level or L level used in aselection line. Therefore, the circuits and wiring for creating powersource voltages can be optimized.

Furthermore, the values of storage capacitance and parasitic capacitancewith respect to the storage capacitor line can be set within a specificrange. This makes it possible to suppress the parasitic capacitance thatdevelops from the storage capacitor line which is not connected to thecircuit for a white pixel from adversely affecting the operation and toensure circuit operation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a configuration of an embodiment.

FIG. 2 shows the signal waveforms of capacitance lines SC-A and SC-B.

FIG. 3 shows the voltage shift states in the case of normally black.

FIG. 4 shows the voltage shift states in the case of normally white.

FIG. 5 shows a planar structure of pixel circuits.

FIG. 6 shows a cross-sectional structure of pixel circuits.

FIG. 7 shows the change in transmissivity for TN liquid crystals and VAliquid crystals.

FIG. 8 shows a configuration of an SC driver.

FIG. 9 shows a structure and operation of a VA mode pixel.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described hereinafter with reference tothe attached drawings.

FIG. 1 is a block diagram of the embodiment. Pixel circuit 1 is arrangedin a matrix on the entire display region. The matrix arrangement mayhave a zigzag form and need not be a perfect lattice. Furthermore, thedisplay may be monochrome or full color. In the case of full color,although the pixels normally have the three RGB colors, it is alsopreferable to add specific color pixels including white as necessary.

As shown in the figure, one pixel circuit 1 comprises a pixel TFT 10 foreach of n channels with each drain connected to a data line DL, and aliquid crystal element 12 and a storage capacitor 14 connected to thesource of the pixel TFT 10. To the gate of the pixel TFT 10 is connecteda gate line GL disposed at each horizontal scan line. A gate capacitor18 inevitably develops between the gate and source of the pixel TFT 10.

The liquid crystal element 12 is configured so that a pixel electrodeprovided individually at each pixel is connected to the source of thepixel TFT 10, and opposed to this pixel electrode so as to sandwich aliquid crystal material is disposed a common electrode for all pixels.The common electrode is connected to a common electrode power sourceVcom.

Furthermore, the storage capacitor 14 has one electrode which is anextension of the semiconductor layer forming the source of the pixel TFT10 and a counter electrode which is part of a capacitance line SC formedin opposition via an oxide film. The parts that form the electrodes ofthe storage capacitor 14 may be separated into a different semiconductorlayer from that of the pixel TFT 10 with both connected by metal wires.

Two capacitance lines SC, SC-A and SC-B, are provided for one line(horizontal scan line), and in the direction of the horizontal scan, thestorage capacitor of each pixel circuit alternately connects to SC-A andSC-B. The storage capacitor 14 of the pixel circuit shown on the leftside in the figure is connected to the capacitance line SC-A and thestorage capacitor 14 of the adjacent pixel is connected to thecapacitance line SC-B.

Furthermore, in this pixel, the capacitance line SC-B is not connectedbut passes through the pixel region. Therefore, a parasitic capacitance16 develops between the pixel electrode of the liquid crystal element 12and the capacitance line SC-B.

To the gate line GL is connected a vertical driver 20. The verticaldriver 20 sequentially selects and sets to an H level one gate line GLat a time at each horizontal period. The vertical driver 20 has a shiftregister so that when a signal STV indicating the start of one verticalscan period is received and the first stage of the shift register is setto the H level, the H level is shifted one at a time thereafter by aclock signal, for example, so that the gate line GL for each horizontalscan line is selected and set to an H level one line at a time. As anexample herein, the H level for the gate line GL is the VDD potentialand the L level is the VSS potential. These power source voltages VDDand VSS are supplied to the vertical driver 20 so that the H level and Llevel are set for the gate line GL, which is the output of the verticaldriver.

An SC driver 22 outputs two voltage levels to two storage capacitorlines SC-A and SC-B.

Namely, in this embodiment, the SC driver 22 receives the supply of twovoltage levels, V_(SC) (H) and V_(SC) (L), from a voltage generatorcircuit 24 for use in controlling the voltages of the two storagecapacitor lines SC-A and SC-B. Furthermore, the voltage generatorcircuit 24 generates V_(SC) (H) and V_(SC) (L) on the basis of presetdata stored in a data memory 26.

The preset data within the data memory 26 can be rewritten by a settingsignal that is supplied from an external source, and the preset datacorresponding to the setting signal is stored into the data memory 26.The voltage generator circuit 24 generates V_(SC) (H) and V_(SC) (L) onthe basis of preset data stored in the data memory 26. Therefore, V_(SC)(H) and V_(SC) (L) can be set by the setting signal. The voltagegenerator circuit utilizes V_(SC) (H) and V_(SC) (L) from VDD and VSSand uses a constant voltage generator circuit to generate V_(SC) (H) andV_(SC) (L). For a simple configuration, a resistive potential divider orthe like can be utilized.

It should be noted that the setting signal may be stored into the datamemory 26, such as by serial transfer from an external microcomputer.

The display device usually is provided with adjustment buttons forcontrast and brightness, and the setting signal is determined accordingto their preset values and stored into the data memory 26.

Although not shown in the figure, the display device is also providedwith a horizontal driver, for example, to control the line-sequentialsupply to the data line DL of a video signal that is input. Namely, inthis example, the horizontal driver outputs a sampling clock for eachpixel in accordance with a video signal clock for each pixel. Thissampling clock turns a switch on and off and latches the video signal(data signal) for one horizontal scan line. The data signal for eachpixel in the latched horizontal scan line is output during onehorizontal scan period to the data line DL.

In actuality, there are three types of video signals for RGB and eachpixel in the vertical direction has the same color as one of R, G, or B.Consequently, the data line DL is set with the data signal for one ofthe RGB colors.

The device of this embodiment employs an AC application method for thedot inversion method. Namely, at each pixel (dot) in the horizontal scandirection, the voltage applied to the pixel electrode of the liquidcrystal element 12 is applied as a data signal having an oppositepolarity with respect to the voltage Vcom of the common electrode.

The left side of FIG. 3 shows the data signal based on a first polarityand the hypotenuse of the triangle denoted by Vvideo represents the datasignal (write voltage) corresponding to the brightness. The data signalhas a potential difference (dynamic range) of Vb from the black level tothe white level, and the voltage applied to the pixel electrodesubsequent to shifting is white for the voltage closer to Vcom with thecenter at Vcom and black for the voltage farther from Vcom. Therefore,in this example, the white level is Vcom−Vb/2 and the black level isVcom+Vb/2. Furthermore, at an adjacent pixel as shown on the right sidein FIG. 3, the voltage has a second polarity that is opposite to that ofthe first polarity so that the white level is Vcom+Vb/2 and the blacklevel is Vcom−Vb/2.

As shown in FIG. 2, after the pixel TFT 10 is turned on and the datawrite operation ends, the capacitance lines SC-A and SC-B shift only bya predetermined voltage ΔVsc. In this example, a normally white TNliquid crystal is used. Regarding the pixel on the left side of FIG. 3,the capacitance line SC-A is connected and Vsc shifts only by ΔVsctoward an increase in voltage. Furthermore, regarding the pixel on theright side of FIG. 3, the capacitance line SC-B is connected and Vscshifts only by ΔVsc toward a decrease in voltage.

As a result, as shown in FIG. 3, the data signal applied to the pixelelectrode shifts only by a voltage corresponding to ΔVsc and is appliedacross Vcom. Here, ΔVsc is set as a voltage corresponding to thresholdvoltage Vath where a change in transmissivity starts in accordance withthe voltage applied to the liquid crystal, and the voltage subsequent toshifting makes it possible to perform display operations on the liquidcrystal element 12. Furthermore, the dynamic range of the data signal isset so that the dynamic range subsequent to shifting becomes thepotential difference of the white level from the black level in thedisplay.

In FIG. 3, Va (W) is the amount of shift of the data signal for thewhite level and Va (B) is the amount of shift of the data signal for theblack level. Therefore, these amounts of shift are determined by ΔVsc.Furthermore, Vb is the potential difference (dynamic range) of the blacklevel and the white level of the data signal and Vb′ is the dynamicrange subsequent to shifting.

The use of a normally-black vertically aligned (VA) type is shown inFIG. 4. In this manner, the data signal has the potential difference(dynamic range) of Vb, and the voltage applied to the pixel electrodesubsequent to shifting is black for the voltage closer to Vcom with thecenter at Vcom and white for the voltage farther from Vcom. Therefore,in this example, the black level is Vcom−Vb/2 and the white level isVcom+Vb/2. Furthermore, at an adjacent pixel as shown on the right sideof FIG. 4, the voltage has a second polarity that is opposite to that ofthe first polarity so that the black level is Vcom+Vb/2 and the whitelevel is Vcom−Vb/2.

The voltage value Vpixel of the pixel electrode of the liquid crystalelement 12 subsequent to shifting can be expressed as follows:Vpixel=Vvideo±{(Csc−Cpa}/(Cgs+Clc+Csc+Cpa)}*ΔVsc  (1)

In this embodiment, a TN type normally-white liquid crystal is utilized.A black display operation is performed by the application of a voltage.With the black level voltage with respect to Vcom subsequent to shiftingdenoted by VB and the dynamic range during a write operation denoted byVb, it is necessary to satisfy the following expression to perform theblack display operation.{(Csc−Cpa)/(Cgs+Clc+Csc+Cpa)}*ΔVsc=VB−Vb/2  (2)

Namely, Vb/2 corresponds to the black level voltage with respect to Vcomduring a write operation and VB is the black level voltage subsequent toshifting so that VB−Vb/2 becomes the shift voltage.

Furthermore, the pixel circuit operates on the basis of the power sourcevoltage VDD. Therefore, a shift voltage ΔVsc lower than VDD becomes anoperating condition.ΔVsc<VDD  (3)

Therefore, to satisfy expressions (2) and (3), it is necessary to formthe pixel circuit.

On the other hand, the capacitance Clc of the liquid crystal element 12is determined when panel size, number of pixels, and liquid crystal tobe used are determined. Furthermore, the gate-source capacitance Cgs ofthe pixel TFT 10 is determined when the size of the pixel TFT 10 isdetermined. Therefore, major changes cannot be made in the design stagefor the display panel.

Accordingly, the capacitance Csc of the storage capacitor 14 and thecapacitance Cps of the parasitic capacitance 16 are varied in thisembodiment. Namely, if the capacitance Csc of the storage capacitor 14is increased to a certain proportion or greater compared with thecapacitance Cps of the parasitic capacitance 16, expression (2) can besatisfied even when setting ΔVsc to a small value so that expression (3)can also be satisfied. By then setting ΔVsc to a small value, it ispossible to design for lower power consumption.

Furthermore, setting Cpa so that ΔVsc does not exceed VDD obviates theneed for providing a special power supply for the Vsc voltage generatorcircuit. Furthermore, advantages can be realized, such as lower powerconsumption, improved pixel aperture ratio, and so forth.

The parasitic capacitance 16 is provided at the same level as the gateelectrode and an interlayer insulating film and a planarization film arefound between it and the pixel electrode. Thickening this planarizationfilm makes it possible to reduce the parasitic capacitance 16. On theother hand, to increase the storage capacitor 14, the gate oxide filmmay be made thinner. The capacitance of the storage capacitor 14 can beeasily changed by changing its area. These techniques permit thecapacitances of the storage capacitor 14 and the parasitic capacitance16 to be adjusted.

SPECIFIC EXAMPLE

When configured so that Csc=320 fF, Cpa=10 fF, Clc=430 fF, Cgs=3 fF,ΔVsc=5.58, VB=3.5V, Vb=2.5V, and VDD=8.5V:{(320−Cpa)/(3+430+320+Cpa)}*ΔVsc=3.5−2.5/2Furthermore:ΔVsc<8.5

Therefore, in this case, Cpa<95 fF can be derived for the capacitance ofthe parasitic capacitance 16.

For example, when Cpa is greater than or equal to 95 fF and thiscondition is not satisfied, the shift voltage becomes insufficient andthe black level display is not performed properly.

Furthermore, the voltage value Vpixel of the pixel electrode of theliquid crystal element 12 subsequent to shifting can be expressed asfollows (identical to expression (1) given above):Vpixel=Vvideo±{(Csc−Cpa}/(Cgs+Clc+Csc+Cpa)}*ΔVsc

When Cgs and Cpa are substantially smaller than Csc and Clc, Vpixel canbe expressed as follows:Vpixel□Vvideo±Csc/(Clc+Csc)·ΔVsc

Furthermore, the molecules in the TN liquid crystal are aligned inparallel with respect to the electrodes in the state where voltage isnot applied, at which time the dielectric constant ε_(//) is smallercompared to the dielectric constant ε_(⊥) when the molecules arevertically aligned with respect to the electrodes in the state werevoltage is applied. Namely, ε_(⊥)>ε_(//). Furthermore, Clc, which is thecapacitance of the liquid crystal element, is determined by thedielectric constant of the liquid crystal material. Thus,Clc_(⊥)>Clc_(//).

For this embodiment, a TN-type normally white liquid crystal isutilized. Accordingly, a black display operation is performed by theapplication of a voltage. With the black level voltage with respect toVcom subsequent to shifting denoted by VB, the dynamic range during awrite operation denoted by Vb, the black level voltage shift denoted byVa (B), and the white level voltage shift denoted by Va (W), Va (B) andVa (W) can be expressed as follows:Va(B)=Csc/(Clc _(⊥) +Csc)*ΔVscVa(W)=Csc/(Clc _(//) +Csc)*ΔVscThus, Va (W)>Va (B).Furthermore, the dynamic range Vb′ subsequent to shifting is expressedas follows:Vb′=Vb−{Va (W)−Va (B)}Thus, Vb′<Vb.

From these relationships, changing the magnitude of ΔVsc enables Va (B),Va (W), and Vb′ to be changed.

In this embodiment, as described hereinbefore, Vsc (H) and Vsc (L) arechanged by the setting signal so that the difference of both signals,ΔVsc, is changed. Due to the change in ΔVsc, the brightness and contrastare then adjusted. Namely, the brightness changes as Va (B) and Va (W)change, the contrast changes as Vb′ changes, and the brightness andcontrast are adjusted by the adjustment of ΔVsc.

The pixel circuit operates on the basis of the power source voltage VDD.Therefore, it is preferable for the shift voltage ΔVsc to be lower thanVDD so as to satisfy ΔVsc<VDD.

FIG. 5 shows a schematic planar structure of a display panel. In thismanner, the DL data line is disposed for each column in the column(vertical scan) direction and two capacitance lines, SC-A and SC-B, aredisposed at each row in the row (horizontal scan) direction.

Although the DL data lines have a linear form and the same width, thisis not necessary. Due to light shading between pixels, it is preferableto widen the line width at those points when DL data lines are used.Furthermore, in the case of a delta arrangement, the DL data linesinevitably become curved.

Furthermore, the capacitance lines SC-A and SC-B widen at the placeswhere the storage capacitor 14 is formed to yield the capacitance.Moreover, in this example, part of the adjacent pixel is also utilizedfor the storage capacitor 14. Namely, by extending the semiconductorlayer (electrode on the opposite side of the storage capacitor lineSC-A) that forms the storage capacitor 14 in the pixel on the left sideof the figure, parts between pixels and of adjacent pixels are alsoutilized for the storage capacitor 14. Furthermore, as will be describedhereinafter, the lower part of the data line is also utilized as part ofthe storage capacitor 14.

It is preferable to narrow the line widths only at the intersectionsbetween the DL data lines and the storage capacitor lines SC-A and SC-Bso as to reduce the areas at these intersections.

The areas at the intersections of the storage capacitor lines SC-A andSC-B and the DL data lines are made uniform. As a result, the values ofthe parasitic capacitances formed from the storage capacitor lines SC-Aand SC-B with the DL data lines become uniform and the fluctuations inpotential of the DL data lines during inversion of the storage capacitorlines SC-A and SC-B can be reduced so as to minimize any adverse effecton the display.

FIG. 6 shows a cross section of a part where one storage capacitor lineSC is disposed. In this manner, on a glass substrate 100 is provided abuffer layer 102 on which is provided a semiconductor layer SCL.Although the semiconductor layer SCL forms the pixel TFT 10, the partshown forms the storage capacitor 14. On the semiconductor layer SCL isformed an oxide film 104. The oxide film 104 is formed by a processidentical to that for the gate oxide film of the pixel TFT 10. On thegate oxide film 104 is formed the storage capacitor line SC. The storagecapacitor line SC is formed by a process identical to that for the gateelectrode of the pixel TFT 10.

On the storage capacitor line SC is formed an interlayer insulating film106 on which the data line DL is formed.

Furthermore, a planarization layer 108 is formed to cover the data lineDL and on it is formed a pixel electrode 30. Although not shown, aliquid crystal layer is provided via an alignment film the pixelelectrode 30 and on it is disposed an opposing substrate formed with acommon electrode to sandwich the liquid crystal layer.

In this manner, the storage capacitor line SC and the data line DLoppose each other via the interlayer insulating film 106 at theintersection. Therefore, a capacitance develops at this part. In thisexample, the semiconductor layer SCL extends below the intersection andis utilized as part of the storage capacitor 14.

Furthermore, FIG. 7 shows the transmissivity with respect to an appliedvoltage to the TN liquid crystal and to the VA liquid crystal. In thecase of the TN liquid crystal, as the voltage applied to the liquidcrystal is raised, the initial transmissivity is at a certain high level(white level), and when the voltage applied to the liquid crystalexceeds a threshold voltage, the transmissivity begins to decrease.Thereafter, the transmissivity decreases at a certain rate until acertain low level (black level). On the other hand, in the case of theVA liquid crystal, when the voltage applied to the liquid crystal israised, the initial transmissivity is at a certain low level (blacklevel), and when the voltage applied to the liquid crystal exceeds athreshold voltage, the transmissivity begins to increase. Thereafter,the transmissivity increases at a certain rate until a certain highlevel (white level).

Furthermore, although the voltage range (dynamic range) necessary forthe display in the TN liquid crystal and in the VA liquid crystaldiffers as shown in FIG. 7, the voltage range can be adjusted bychanging ΔVsc in this embodiment.

In the SC driver 22 in this embodiment, the power source voltages VDDand VSS used in the vertical driver 20 or the voltages input by thepanel are utilized for the H level voltage (V_(SC) (H)) and/or L levelvoltage (V_(SC) (L)) in the capacitance lines SC (SC-A or SC-B). BesidesVDD and VSS, a GND potential is also supplied to the vertical driver 20.Namely, the vertical driver 20 includes the shift register for drivingthe gate line GL and utilizes the GND potential in the shift register.Accordingly, the GND potential can also be used for one of either the Hlevel voltage (V_(SC) (H)) or the L level voltage (V_(SC) (L)).Moreover, another potential is usable provided that potential is inputby the panel. Therefore, it is preferable to utilize the potentialsutilized in the vertical driver 20 for both the H level voltage (V_(SC)(H)) and the L level voltage (V_(SC) (L)) in the SC driver 22. In thedescription hereinafter, an example is given where VDD or VSS isbasically utilized for either the H level voltage (V_(SC) (H)) or the Llevel voltage (V_(SC) (L)).

Namely, as shown in FIG. 8, a display control signal, which becomes an Hlevel, is supplied to the control terminals of switches SW1 and SW2 forthe period where the H level is supplied to the capacitance line SC.Switches SW1 and SW2 are respectively an n-channel TFT and a p-channelTFT connected in parallel. The gate of the p-channel TFT of switch SW1and the gate of the n-channel TFT of switch SW2 are connected and tothis connection is supplied a display control signal that has beeninverted by an inverter. The display control signal is supplied to thegate of the n-channel TFT of switch SW1 and the gate of the p-channelTFT of switch SW2. Furthermore, VDD or V_(SC) (H) is input by the inputof switch SW1 and V_(SC) (L) or VSS is input by the input of switch SW2,for example. The outputs of switches SW1 and SW2 are connected to thecapacitance line SC-A or SC-B.

Namely, although the SC driver 22 requires two voltages to drive thecapacitance lines SC-A and SC-B, either one or both voltages in thisembodiment is set as VDD or VSS to be utilized in the vertical driver20. For example, when V_(SC) (L) is utilized for the L level, the Hlevel is VDD, and when V_(SC) (H) is utilized for the H level, the Llevel is VSS or the voltage that is input by the panel. Therefore, sinceonly one of either V_(SC) (H) or V_(SC) (L) and not both need begenerated, the power source circuit can be simplified. Furthermore,since the SC driver 22 is provided in proximity to the vertical driver20, the wiring for VDD or VSS to be input by the vertical driver 20 forinput by the SC driver 22 may be short.

For the circuit shown in FIG. 8, one circuit is provided per capacitanceline SC (SC-A or SC-B). V_(SC) (L) is determined with respect to VDD orVSC (H) is determined with respect to VSS so that, for example, thedifference between the H level and the L level becomes ΔVsc.

Due to the circuit of FIG. 8, when the display control signal is at theH level switch SW1 turns on so that V_(SC) (H), for example, is output,and when the display control signal is at the L level, switch SW2 turnson so that V_(SS), for example, is output.

The configuration and operation of a pixel in a VA mode display deviceusing VA liquid crystals are described herein with reference to FIG. 9(a) to FIG. 9 (c).

FIG. 9 (a) and FIG. 9 (b) are schematic cross sections of the VA modeliquid crystal display device (LCD) using VA liquid crystals along lineA-A of the LCD having the schematic cross section shown in FIG. 9 (c).This LCD normally employs a rubbing-less type alignment film where arubbing process is not performed. For this reason, the initial alignmentof the liquid crystal has no pre-tilt angle, and when voltage is notapplied, the direction of the major axis of the liquid crystal moleculeis aligned facing the normal line of the substrate. As shown in FIG. 9(a) and FIG. 9 (b) where a liquid crystal molecule 60 is initiallyaligned in the vertical direction, as a voltage is applied between thepixel electrode 30 and a common electrode 40 of the LCD, a weak electricfield (refer to electric lines of force indicated by dotted lines in thefigure) generated in a state of low initial voltage is tilted at anangle, such as at the end of the pixel electrode 30. The direction alongwhich the liquid crystal molecule slants following the rise in voltageis defined according to this tilted electric field.

As shown in the figure, an alignment dividing part 50 is provided withinthe region for each one pixel so that a plurality of regions within theone pixel region can be divided into various directions. In the exampleof FIG. 9 (a)-(c), the alignment dividing part 50 is formed by providingprojections on electrodes and electrode-free regions (windows) so that apattern extends in the form of polygonal lines respectively in thevertical direction on the screen for both the common electrode 40 andthe pixel electrode 30. It should be noted that the alignment dividingpart 50 is not limited to this pattern and may be formed, for example,by providing electrode-free regions (windows) and projections in apattern where the lengthwise top end and bottom end within one pixel aredivided in a forked manner. Due to the alignment dividing part 50 asshown in FIG. 9 (a) and FIG. 9 (b), the boundary of the liquid crystalalignment direction within one pixel can be fixed at the dividing part50, and the boundary position within the pixel of the direction in whichthe liquid crystal molecule tilts differs depending on the pixel and theparticular drive timing so as to prevent an adverse effect on thedisplay quality, such as display flickering.

In the embodiment, the display operation is performed only by the lightfrom a light source, such as one disposed in the back of the panel, sothat it is applicable to any type of transmissive LCDs employingtransparent conducting electrodes, such as ITO, for both the pixelelectrodes and common electrode, reflective LCDs that perform displayoperations by reflecting ambient light using reflective metal electrodesfor the pixel electrodes, and also semi-transmissive LCDs that functionin a transmissive mode when a light source is used and in a reflectivemode when the light source is turned off. Although improvements, such asgreater contrast, are demanded in reflective LCDs and semi-transmissiveLCDs, performing polarity inversion as in the embodiment makes itpossible to perform display operations at a sufficiently high contrasteven with reflective or semi-transmissive LCDs in the ECB mode, forexample.

1. A display device having pixel circuits disposed in a matrix, eachpixel circuit comprising: a pixel TFT that is turned on and off byconnecting one end to a data line for supplying a data signal,connecting a gate to a selection line, and setting a selection signal onthe selection line to an H level or an L level; a storage capacitor forstoring a voltage of the data signal supplied from the data line, oneend of which is connected to another end of the pixel TFT and the otherend of which is connected to a storage capacitor line; and a liquidcrystal element for applying a voltage to a liquid crystal betweenelectrodes, one electrode of which is connected to said another end ofthe pixel TFT and the other electrode of which is held at a commonelectrode potential; wherein said storage capacitor line, after saidpixel TFT is turned on and the data signal on the data line is writtento the storage capacitor, changes from a first level to a second level;and either said first level or said second level is used in common withone of a plurality of voltage levels which are used in vertical driverwhich drives the said selection line.
 2. A display device according toclaim 1, wherein: two types of data signals having opposite polaritieswith respect to said common electrode potential are supplied to saiddata line; said storage capacitor line is provided with two lines tocorrespond to each pixel circuit row, a plurality of pixel circuitsdisposed in a row direction are connected to at least one of the twostorage capacitor lines and said two storage capacitor lines arecontrolled by two types of potentials; and the potential of said twostorage capacitor lines is set in accordance with said data signal thatis supplied in each pixel circuit.
 3. A display device according toclaim 2, wherein: when one potential of said two types of potentialsshifts in a positive to negative direction or a negative to positivedirection, the other potential shifts in an opposite direction.
 4. Adisplay device according to claim 2, wherein: said two storage capacitorlines are connected alternately to each pixel circuit in the rowdirection.
 5. A display device according to claim 2, wherein: theexpressions (i), (ii) below are satisfied{(Csc−Cpa)/(Cgs+Clc+Csc+Cpa)}*ΔVsc=VB−Vcont/2  (i)ΔVsc<VDD  (ii) where capacitance of said storage capacitor is C_(SC);parasitic capacitance developed at a node of said pixel electrode andsaid storage capacitor line connected to an adjacent pixel circuit isCpa; gate-source capacitance developed at a node of said pixel electrodeand the gate of said pixel TFT is Cgs; capacitance of said liquidcrystal element is Clc; voltage value to be shifted in said storagecapacitor line is ΔVsc; potential difference of a black level voltageand a white level voltage of said data signal is Vcont; a black levelvoltage subsequent to voltage shifting is VB; and voltage of a powersource supplying power to operate pixel circuits is VDD.
 6. A displaydevice having pixel circuits disposed in a matrix, each pixel circuitcomprising: a pixel TFT that is turned on and off by connecting one endto a data line for supplying a data signal, connecting a gate to aselection line, and setting a selection signal on the selection line toan H level or an L level; a storage capacitor for storing a voltage ofthe data signal supplied from the data line, one end of which isconnected to another end of the pixel TFT and the other end of which isconnected to a storage capacitor line; and a liquid crystal element forapplying a voltage to a liquid crystal between electrodes, one electrodeof which is connected to said another end of the pixel TFT and the otherelectrode of which is held at a common electrode potential; wherein saidstorage capacitor line, after said pixel TFT is turned on and the datasignal on the data line is written to the storage capacitor, changesfrom a first level to a second level causing a voltage to be applied tothe liquid crystal element to shift; said storage capacitor line isprovided with two lines to correspond to each pixel circuit row, aplurality of pixel circuits disposed in a row direction are connected toat least one of the two storage capacitor lines and the two storagecapacitor lines are controlled by two types of potentials; and theexpressions (i), (ii) below are satisfied{(Csc−Cpa)/(Cgs+Clc+Csc+Cpa)}*ΔVsc=VB−Vcont/2  (i)ΔVsc<VDD  (ii) where capacitance of said storage capacitor is C_(SC);parasitic capacitance developed at a node of said pixel electrode andsaid storage capacitor line connected to an adjacent pixel circuit isCpa; gate-source capacitance developed at a node of said pixel electrodeand the gate of said pixel TFT is Cgs; capacitance of said liquidcrystal element is Clc; voltage value to be shifted in said storagecapacitor line is ΔVsc; potential difference of a black level voltageand a white level voltage of said data signal is Vcont; a black levelvoltage subsequent to voltage shifting is VB; and voltage of a powersource supplying power to operate pixel circuits is VDD.
 7. A displaydevice according to claim 6, wherein: when one potential of said twotypes of potentials shifts in a positive to negative direction or anegative to positive direction, the other potential shifts in anopposite direction.